1. Field of Invention
This invention relates to a wafer level assembly package. More particularly, the present invention is related to a wafer level assembly package having a wafer with a protection layer formed on the back surface thereof.
2. Related Art
As shown in FIG. 1, it illustrates an enlarged portion of a conventional semiconductor wafer 10. Generally speaking, said semiconductor wafer 10 has a back surface 102, an active surface 104 and a plurality of bonding pads 106 formed on the active surface 104. The wafer level assembly package is formed by the steps of forming an under-bump-metallurgy (UBM) layer 12 on the bonding pad 106, forming a solder bump 14 on the UBM layer 12 and reflowing the solder bump 14 to secure to the UBM layer 12 as show in FIG. 2. Referring to FIG. 3, usually, a thermally conductive layer 18, for example a metal layer, is formed on the back surface 102 of the semiconductor wafer 10 for thermal enhance. Afterwards, a laser is performed to form a melted portion 182 and an un-melted portion 184. In such a manner, a logo is formed on the back surface 102 of the semiconductor wafer 10 due to the contrast between the melted portion 182 and the un-melted portions 184.
However, the solder material has a good wettability with the metal layer. Specifically, the solder material has a better wettability with the gold metal layer. Accordingly, when the solder bump 14 is formed on the active surface 104, the excessive solder material is reacted with the gold metal layer 18 formed on the back surface 102 so as to make the solder material located on the back surface 102 of the wafer 10 and cause the back surface 102 to be easily contaminated. In addition, the logo is formed by laser marking the metal layer on the back surface. However, the contrast between the melted portions and un-melted portions is not apparent, so the logo is not well identified.
Therefore, providing another assembly package to solve the mentioned-above disadvantages is the most important task in this invention.